The present disclosure relates to a calibrating system for an infrared (IR) sensor or any broadband detector responsive to electromagnetic radiation from varying radiation source types.
Detectors typically include an array of pixels, each pixel being operable to generate or pass a current in response to electromagnetic energy incident upon the pixel. In most cases the generated or passed current is proportional to the incident energy.
These pixels are prone to some fluctuation in their response behavior over the life of the detector. Regular calibration is typically desirable so as to ensure uniformity in measurements. It is important to know the relative operation performance of the pixels relative to themselves. An unknown change in performance could lead to erroneous data regarding measurements of an electromagnetic energy source. As such, calibration is used to correct for pixel to pixel variations, such as a non-uniformity correction, and changes in the pixel response over time.
Typically, the calibration is accomplished by placing source(s) at or near the detector. The source illuminates the detector. Although calibration in a laboratory environment is typically performed before deployment, regular re-calibration after deployment is highly desired for the reasons stated above.
As detector assemblies of this type are frequently used in space based devices, a complex calibration system is quite undesirable. Size and weight are ever present factors in the cost of assembly and launch. The greater one component is in terms of size and weight, generally the smaller some other component must be.
Further, the system must also be designed to withstand the forces encountered during launch and deployment and then repeated operation requests without being easily serviceable. There are also a number of existing elements that are highly desired for detector functionality, such as spectral filter wheels and guidance systems. Options to provide calibration without compromising existing systems has proven challenging as well.
FIGS. 1 and 2 illustrate conventional system 100 used for calibrating detector 102. FIG. 1 illustrates system 100 in a non-calibration mode of operation, while FIG. 2 illustrates calibration system 100 in a calibration mode of operation.
System 100 includes source assembly 108 having one or more light sources 112 (e.g., light sources 112A-C), mirror 110 and detector 102. Light source 112 is configured to emit light. Mirror 110 is configured to receive the light from source 112 and redirect or reflect the light to detector 102.
System 100 also includes two mechanisms that are used for calibrating detector 102. These mechanisms include source assembly rotation mechanism 104 and mirror rotation mechanism 106. Source assembly rotation mechanism 104 rotates or moves light source 112 to illuminate mirror 110 and thus detector 102. That is, source assembly rotation mechanism 104 directs the Field of View (FOV) of detector 102 at source 112. Mirror rotation mechanism 106 rotates or moves mirror 110 into the incoming light path from source 112 so that mirror 110 receives the light from source 112, and redirects that light onto detector 102.
During calibration mode of system 100, as shown in FIG. 2, source 112B is moved or rotated by source assembly rotation mechanism 104, and mirror 110 is moved or rotated by mirror rotation mechanism 108 such that the light emitted by source 112B is received by mirror 110, and the received light is reflected by mirror 110 onto detector 102. Also, during calibration mode, source 112A and mirror 110 are moved or rotated such that the light emitted by source 112A is received by mirror 110 and reflected by mirror 110 onto detector 102, while source 112C and mirror 110 are moved or rotated such that the light emitted by source 112C is received by mirror 110 and reflected by mirror 110 onto detector 102.
These two discrete mechanisms (i.e., source assembly rotation mechanism 104 and mirror rotation mechanism 106) used for calibrating detector 102 add complexity to system 100 and introduce additional reliability concerns over a single mechanism.
Embodiments of the present disclosure provides improvements over the conventional calibrating systems.